1. Field of the Invention
The present invention concerns a method and a system for the packing of items in bags of foil, which in a coherent web are fed through a filling station in which a filling of the individual bags is effected, and which are then closed and separated from the coherent web in the formation of individual packages.
2. Description of Related Art
A basic example of this technology is described in EP 696997, where it is disclosed that the opposing upper edge areas of the bag web are provided with bent-over channel-forming edge parts for drawing in on carrier rods, which in the feeding direction have a mutual enlargement to bring about an opening of the bags, so that these can be filled, e.g. through an overlying filling funnel, after which the carrier rods are again drawn in towards one another for provisional closing of the filled bags. The bags can then finally be closed by being welding together down under the said channel part, after which they are cut over and mutually separated. It is disclosed as an alternative that instead of the channel parts, use can be made of thickened edges which can be introduced into slotted carrier tubes for a quite corresponding feeding forwards of the bags.
There have since been suggested other forms of means used for the gripping and supporting of the opposing upper edges of the bag web, e.g. as disclosed in EP 0 555 321 B, where use is made of special gripping chains for this purpose, without any special requirements concerning the configuration of the upper edge areas of the folded bags. This is of particular importance, in that as starting point a simple, rolled-up web of flat foil without local thickenings can be used, but on the other hand there are considerable problems both with regard to the control of the opposing bag edges for secure engagement with the gripping chains and with regard to a desirable inexpensive configuration of these chains.
Moreover, in EP 0 825 116 it is disclosed that operations can be carried out with a closed, flat tubular web of foil, which can e continuously cut up along its upper edge, with associated integrated folding out and gripping of the upper edges thus cut up, without these being specially configured either as channels or with thickenings, which constitutes a distinct simplification of the requirements concerning the formation of the bag web. The cut-up upper edge parts are folded out for clamping between respectively moved belts which are provided with longitudinal depressions and corresponding pressing-in strings, whereby a suitably firm support engagement can be established.
However, this engagement is no more firm than axial slipping can occur between the upper edges of the bag web and the associated belt conveyor means, whereby uncertainty can arise concerning the degree to which an item being fed has been fed forward with the conveyor belts in a fully synchronous manner. Moreover, deviations can arise with regard to the height at which that area of the web sides which are clamped between the conveyor belts lies, which can be of significance with regard to whether the filled bags are finally closed at precisely the place at which the closure is intended, e.g. seen in relation to printing on the bag.